Signal transduction, an important mechanism in a variety of cellular processes (e.g. protein biosynthesis, hormone stimulated metabolic activities, muscle contraction, etc.), is carried out in part through protein conformational changes induced by nucleoside triphosphate binding and hydrolysis. The Fe protein in nitrogenase is one member of this class of proteins. Although structures exist for nitrogenase component proteins, the factors affecting conformational change and MgATP hydrolysis are not well understood. The major objectives of this proposal are to use biochemical, biophysical, and computational techniques (x- ray crystallography, small angle x-ray scattering, calorimetry, and QM/MM calculations) to define conformational changes in the Fe protein during nucleotide binding, hydrolysis, and signal transduction as well as effects of amino acid environment on modulating [4Fe-4S] cluster properties. [unreadable] [unreadable] [unreadable]